A method and apparatus for making a pipe to plate joint have been used in shipbuilding for various purposes such as supporting light fixtures. Light fixtures on ships are hung from the overhead at the ends of two lengths of pipe called "stools" in the trade. The stools are attached to the overhead structure by welding. Depending on the application, the weld may be a tack weld at a couple of points on the circumference of the stool, or a complete circumferential fillet weld. Depending on the method used, this may require one person to hold the stools to the overhead with a special jig while a welder tacks the stools to the structure. The jig supports the two stools to insure that they are positioned correctly to fit the light fixture. The jig is then removed and, if necessary, the stool welds are completed. If the overhead is of a special material, for example, high yield steel, special welding procedures must be followed to avoid a reduction in the characteristic qualities of the steel. These special procedures may be very cumbersome and time-consuming, requiring specially qualified welders and lengthy inspections and auditing steps. Some materials used for the overhead also require heating prior to welding which can be a very expensive additional procedure.
After the stool is welded to the overhead, a piece of flat bar is attached to the lower end of the stool by any appropriate method. For example, the flat bar may be welded to the stool in advance, or may be attached later by welding or other appropriate method.
The light fixture, for example, a fluorescent fixture, is then attached to the flat bar by conventional means. Depending on the size of the fixture, one or more stools may be used; if only one, a jig may not be necessary. The length of the stool(s) will depend on the standoff desired from the overhead.
In certain shipbuilding applications, it may be required to move the fixture at some later time. To accomplish this movement, stools must be cut from the overhead, and the welds ground until smooth. If the overhead is of a special material, cumbersome weld repair, inspection and auditing steps may again be required.
The prior art has made attempts to provide plate and pipe joints to form an overhead hanger and such has been disclosed in the recent U.S. Pat. No. 4,667,916 issued May 26, 1987. Each of the disclosed forms of the patented invention represent notable disadvantages in that they require significantly more swaging of the pipe. For instance, in the patented embodiments the pipe must be swaged both above and below the insert and actually reduced in diameter or to two different diameters. Such a swaging would require a significantly heavier press and would take significantly greater time. Further, the patented invention exhibits a disadvantage of having the insert either positioned accurately in the pipe for a one-step swaging operation which slows down the operation or a lower swage must be made and the insert pushed in the pipe and thereafter an upper swage made, obviously these steps require more cumbersome operation. Further disadvantages of the patented invention are that there may be insufficient capture of the insert to prevent rotational movement. Further in one of the embodiments of the patented invention, the pipe stool must be threaded internally, which when considering different lengths of pipe that may be required, would be a more cumbersome process than simply threading the inserts. Such threads on the pipe would also weaken the wall of the pipe stool and form stress risers.